Field of the Invention
The present invention relates generally to a lithographic apparatus, and more particularly to an actuation system and a lithographic apparatus having the actuation system.
Background Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
Some moving parts of the lithography apparatus are powered by a high voltage power supply. Furthermore, for some lithographic processes, parts of the lithography apparatus are kept at very low pressure. In Extreme Ultraviolet (EUV) lithography, the lithography process is performed at very low pressure in order to decrease the absorption of the EUV radiation by air. In particular, at very low pressure, a high voltage power supply may be used to power any actuators that are used to position the table on which the substrate is placed, any so-called blades that block a portion of the projection beam or any clamps that hold the mask or the substrate to a table that may be part of the lithography apparatus. Due to the fact that high voltage is used, and in particular because the components are situated in a very low-pressure environment, there is a problem that electrical breakdown may occur (Paschen effect). The possibility of electrical breakdown limits the voltage of the power lines and presents a safety hazard and a lifetime issue. If a full insulation breakdown occurs, it can pollute surfaces of optical components, create electromagnetic interference that disturbs sensitive electronics, cause severe machine damage and present a human safety hazard. Even with partial discharges (ionization corona effect), part of the power line insulation material will be gradually broken down into gaseous form which can also cause pollution of surfaces of optical components and will cause electromagnetic interference to sensitive electronics.
Another issue is that of the uncontrolled return of common mode currents. Common mode currents arise from motion control systems with electric motors (e.g., Wafer Stage). Measurements have shown that the resolution of sensor systems in the machine is deteriorated due to these common mode currents, which interfere with the sensor systems.